Azeotropic distillation of butadiene and 2-butene



rPatented Dea-17, 1946 f. UNITED STATES PATENT ol-FlcE AzEoTnoPro ms'rLLA'rroN or' BUTADIENE AND z-BUTENE Frederick E. Frey, Bartlesville, okle., assigner to Phillips Petroleum Co Delaware mpany, a corporation oi' Application March 13, 19414, Serial No. 383,235

` 7 claims. (crane-42) This invention relates to the concentration of diolefln hydrocarbons. It relates further to the concentration of low boiling vdioleilns, more particularly butadiene, from mixtures containing athen hydrocarbons of closely adjacent boiling points. As one modication, it relates to the production of a normal C4 hydrocarbon mixture by the dehydrogenation of normal butane and the separation of a butadiene concentrate therefrom.

. dure is one of the more direct ways of producing dioleins it has not yet found very extensive commercial application, and one of the obstacles in its commercial development has been the diniculty of eiecting separation of oleilns and diole` iins from each other and from mixtures containing the corresponding paratiins;

"In my copending application Serial No. 354,890,

filed August 30, 1940, now Patent 2,371,817, issued March 20, 1945, I have disclosed a process of producing Alow boiling dioleflns from the corresponding' paramns in which a single dehydrogenation step is employed. As discussed therein, this dehydrogenation step apparently does not form the major part of the diolein product by a dehydrogenation of a paraflln directly to a dioleiin with no intermediate reactions, but apparently cooperates with the rest of the process to eiect a destantially all the normal butane, l-butene and I have now found that elcient separation of butadiene from aA C4 fraction of the eilluent of such a dehydrogenation process can be readily carried out, and thebutadiene recovered in a state of high purity, by a series of fractional distillation steps, in the 'rst of 'which sulfur dioxide is present in a limited amount, and in the second of which essentially no sulfur dioxide is present. While my separation step is quite advantageous- 1y combined with a step for the dehydrogenation of normal butane to produce butadiene such as is disclosed in my copending application, itis understood that in its broadest modication my separation step can operate on any C4 fraction which contains butadiene and other C4 hydrocarbons' which are difilcult to remove therefrom.

It has been disclosed in U. S. 2,186,524.. of which I am a coinventor, that sulfur dioxide forms minimum-boiling yazeotropic mixtures with each of the butanes and butenes. I have now found that if a C4 fraction containing butadiene together with normal butane and normal butenes is fractionally distilled in the presence of sulfur dioxide, the amount of sulfur dioxide can be so limited that the overhead fraction contains subsulfur dioxide charged to the distillation, the kettle product will then contain Z-butenes and substantially all the butadiene charged to the process, and butadiene can be separated in a state o f high concentration from this kettle product by subsequent fractional distillation in the absence of sulfur dioxide. In the presence of actinic light `and of certain catalysts butenes and butadiene form sulfones and/or heteropolymeric compounds of extremely high molecular weight. Such reactions are not desirable in connection with my hydrogenationfof paramns to olens and concomitantly a dehydrogenaton of olens to diolens, the latter being produced .in substantial quantities. In this process the dehydrogenation eilluentwill contain predominantly free hydrogen,

and olen and dioleiin hydrocarbonscorresponding to the paraffin hydrocarbon charged to the process, with the olens being present in amounts greater than the amounts of dioleflns, as well as quantities of such paraflin hydrocarbons which are unreacted. In this process unreacted parains and corresponding oleflns areV separated from the 'other products and are* returned to the dehydrogenation along with fresh parailn hydrocarbon material.

" drocarbons without the formation of intermeprocess, and are to be avoided.

It is any object of my invention to produce low boiling dioleflns in high concentration.

Another object of vmy invention is to separate low boiling diolens from other hydrocarbons of closely adjacent boiling points.

A further object voi my invention is to separate dioleflns in high concentration from other hydiate chemical compounds.

Still another object is to separate butadiene from other C4 hydrocarbons.

Another 'object of my invention is to obtain a.

butadiene fraction of high concentration from the dehydrogenation of normal butane.

Further objects and advantages of my invention will become apparent from the accompanying dSQIQSLlre and discussion.

My invention will now be more speclilcally described in connection with the accompanying drawing which shows diagrammatically by way of a flow sheet an arrangement of apparatus for practicing one modification of my invention. In this modification the invention will be described in connection with a dehydrogenation step for producing butadiene from normal butane.

Referring'now to the drawing, a paraffin hydrocarbon material comprising essentially normal butane enters the system through pipe I andV valve I I and is passed at a relatively low pressure to dehydrogenation unit I2. The dehydrogenation unit I2 is comprised of suitable'heating units vor furnaces, catalyst chambers, 'and the like tion is reached only a limitedamount of dehydrogenation per pass will actually take place, since the net. reactin will be the dehydrogenation of a small amount ofl butane to form buteries, and of butenes to form a corresponding amountof butadiene, anda large substantitally adiabatic catalyst chamber may be used with adequate heating of the stream charged to such chamber. The resultant productspass through pipe I3 and valve I4 to the separatirg means I5. In separating means I5, Cs and lighter material including free hydrogen is separated from the C4 hydrocarbons and removed-through pipe I6 and valve I1.

If any C5 and heavier material is present in the eilluent of the dehydrogenation, this material should also be removed, as through pipe I8 and valve I9.

.A` resulting C4 .hydrocarbon ,fraction is passed from separating means I5 through pipe 20 and may be passed through valve 2| to an absorption unit 22. The absorption unit 22 is used to eiect a preliminary concentration of butenes and butadiene, which `may be done by using any suitable absorption operation, but which is more .advantageously accomplished inl combination I* with the present invention by using a liquid sulfur dioxide as a selective absorbent. In such a case sulfur dioxide is passed through pipe 25 and through pipe 26 and valve 21 to a high point of absorber 22 and therein is passed countercurrent as a liquid to a hydrocarbon stream,

introduced through valve 2| as previously described, also. in liquid phase, although it may ,in some instances be in vapor phase. Unabsorbed butane is removed through pipe 28 and may be discharged from the system through pipe 23 and valve 24 or, if desired, may be passed through valve 29 to pipe 51 for recycle within the system, as will be ldiscussed hereinafter.

In the absorption unit 22 liquid sulfur dioxide selectively dissolves normal butenes and buta l diene and will also take up a certain amount of normal butane. The rich absorption liquid is lpassed through pipe 3| and valve 32 to a fractional distillation unit 40.

When a normal C4 fraction is available from any suitable source, such as a fractionobtained .p from the gases resulting from the cracking of heavier oils or in the cracking of light gases to i'orm normally gaseous oleiins, such a material may be charged to the process through pipe 33. and valve 34 and may :loin a C4 fraction passing from the separating unit I5 through pipe 20 or, ii desired.. it may constitute the sole hydrocarbon material charged to the process. If the absorption unit 22 is employed as just discussed, such a C4 fraction may be passed through pipe 35 and valve 38 to pipe 20. However, if it is not desired to use such an absorption means for concentrating the unsaturated hydrocarbons, the Cliractionfmay be passed from pipe 33 through pipe `31 and valve 38 to pipe 3| and on to the fraction distillation unit 40. In many instances when the dehydrogenation unit I2 is used to produce all or part of the butadiene, it will not be necessary to use the absorption unit 22 and the C4 fraction from separating means I5 may be 31 to pipe 3| and the fractional distillation unit 40, as will be readily appreciated.

In'fractional distillation unit 40, which is illustrated diagrammatically as a single fractionating column, a. distillation of the C4 hydrocarbons takes place in the presence of sulfur dioxide, which ,is added in amount suilicient to form azeotropic mixtures with substantially all of the normal butane and l-butene fraction and in an amount so limited that little if any of the Z-butenesior butadiene are included. Sulfur dioxide for this purpose may either enter the distillation column along with the hydrocarbons through pipe 3| from absorption unit 22, or may 35 be introduced separately at one or more other points along the line of the distillation column through pipe 42 and valve v43 and/or at some other part of the column as through pipe 48 and valve 49.` When it is desired toadd sulfur dioxide to the material passing through pipe 3| this may be accomplished by suitable control of valve 4| in pipe 25.

A low boiling mixture containing sulfur dioxide, normal butane and l-butene is passed from the 4i5 top of the fractionating column 40 through pipe 45, cooling and condensing coil 46 and valve'41 to a suitable separating means such as separator 5I). In this separating means a suitable separation may be effected between sulfur dioxide and 50 hydrocarbon constituents passing with it through pipe 45. This may -be accomplished by suitable condensation and subatmospherie cooling to temperatures within the range of about +20 tov 100 F., or by a further azeotropic distillation such as is disclosed in U. S. Patent 2,186,524, or

by vother suitable operations. A sulfur dioxiderich material is passed from separator 50 through pipe 5I and may be discharged from the process entirely or in part through valve 52. Generally, 30 however,l a substantial portion thereof will be l returned to the fractionating column 40 through pipe 53 and valve 54 as a liquid ,.reux. If the olefin content of this stream tends to build up too high a value, such material may be removed through valve 52 for a further separation of more or less pure sulfur dioxide which may be reintroduced in the system through pipe 25.

Hydrocarbon material separated from sulfur dioxide in separator 50 may be removed through pipe 55 and may be passed entirely or in part from the system through valve 56. However, when dehydrogenation unit I2 is a part of the process, it will generally be desirable to recycle all or a part of the hydrocarbons contained in 15 this material to this dehydrogenation, and this .passed directly through pipe 20, pipe 35 and pipe alkali solution such as sodium hydroxide or may be effected by passing4 any desired portionl -of the stream from pipe 55 through pipe 51 and through valve 58 to pipe I0. Ii' this stream` timate contact by the reilux liquid and ascending contains an appreciable proportion of sulfun J dioxide, this should be removed before the material is passed to the dehydrogenation unit.`

sodium carbonate may be passed to the scrubber through pipe B13-and valve 64 to effect the removal of sulfur dioxide from the hydrocarbons treated therein and t'ne contaminated scrubbing medium may be removed through pipe 65 and e .valve 66 for regeneration or such other treatment as may seem desirable. Other suitable means for separating hydrocarbons from sulfur dioxide may be used, as may seem desirable or expedient.

From the bottom of fractional distillation means 40 a. `kettle product,lwhich will comprise essentially Zf-butenes andbutadiene and which should be substantially free of sulfur dioxide, is passed through pipe and valve 1I to a second fractional distillation means 412. If there is suillclent sulfur .dioxide in this material to reduire its removal, this may be accomplished by passing the stream from pipe 10 through pipe 13 and valve 14 for suitable puriiication as by treatment with a suitable scrubbing medium in scrubber 15.`

A suitable scrubbing medium may be added through pipe 80 and valve 92, and the spent scrubbing medium may be removed from the system through pipe 18 and valve 19. The purified hydrocarbon material is passed through pipe 16 and valve 11 back to pipe 10 and fractional distillation means 12, valve 1I being closed.

The fractional distillation unit 12 is so operatedas to effect a separation of a substantially pure butadiene fraction, which should generally contain more than 90 per cent butadiene and preferably more than 95 per cent butadiene, afithough a lpurity greater than about 98 per cent will generally not be necessary. This fraction is removed as an overhead product through pipe 8| and valve 82 for whatever subsequent use may be desired. The kettle product, which will contain substantial quantities of Z-butenes, is removed through pipe 83 and may be discharged from the system through valve 84. In one modiflcation of my process it may be desirable to pass a portion of this-kettle productv back to the fractional distillation unit 40, and this may be accomplished by passing the desired portion through pipe :85, pipe 81 and valve 88 to a point in the 3upper portion o-f the fractional distillation unit 40, or as may be found more desirable in some particular instance, it may be passed from pipe 81 through pipe 89 and valve 90 to a point in the lower part of this fractional distillation unit. When the dehydrogenation unit l2 is a partof my process and this kettle product does not contain too high a concentration of butadiene, a portion of it may be passed through valve 86 in a continuation of pipe 85 to pipe I0.

While fractional distillation units 40 and 12 have been shown as single units, it is to be understood that this is merely diagrammatic and either one or both of them may comprise two or more fractional distillation columns, each with suitable bubble trays or packing not shown, to afford invapors with suitable heating means for the kettle, and cooling nrieans for the top, reflux accumulators and reux lines and thelike as will be readily understood by'one skilled in the art. It win be e' desirable that the butadiene-containing material, especially when the butadiene is int a somewhat concentrated state, should notbe heated to too high a temperature since this material "polymerizes somewhat readily. `It is well known that sulfur dioxide forms sulfones and high .molecular weight heteropolymeric compounds with butenes and butadiene. Such chemicalfreactions take place in the presencev of actinic light and also in the presence of certain catalysts and are to be avoided. In some instances it may be necessary to add materials to inhibit the forma- .butadiene as a kettle product, at times a better tion of such compounds, such as phenyl-betanaphthylamine, pyrogallic acid, hydroquinone, catechol, resorcinol, cresols and similar phenolic compounds. Any iso-C4 hydrocarbons present in the charge to fractionating means will be removed therefrom in`the overhead product, and Lmay be discharged from the system through valves 52 and/or 56. some or'all of any iso-Css present inthe material charged to lseparating means I5 may be removed, as a part of the Ca materiaLthrough pipe I6.

of the 2butenes bewseparated along with the separation can be effected if a small portion of the 2.butenes, especially the trans-isomer, is permitted to pass from the ldistillation column 40 through pipe as ,a part of the overhead product.

As an example of my process, a C4 hydrocarbon fraction containing about 'I per cent butadiene, 25 per cent normal butenes of which about onefourth is 1butene and three-fourths 2-butenes, and 68 per cent no al butane may be passed as a liquid to a fractionaldistillation column of 100 plates (and in two sections operated under a `total column pressure of about 120 pounds per square inch. Sulfur dioxide is introduced to the column in two places, the major, part being returned as reilux at a point near the top, with sufficient make-up being addedA along with the C4 stream to give a total amount of sulfur' dioxide introduced equal to about 10 per cent in excess of that required to form azeotropic mixtures with the normal butane and l-butene introduced, under the conditions existing at the top of the column. Under these conditions a small amount of 2-butene, primarily vthe trans-isomer, is included in the overhead product. Asulfur dioxiderich fraction is separated from the overhead product and returned vto the column as a liquid reilux, thereby controlling the top temperature and furnishing sulfur dioxide for the azeotropic distillation. A kettle product comprising primarily 2butenes and butadiene is freed from traces of sulfur dioxide and passed to a second fractional 4distillation column, containing 120 plates in three sections. This column is operated at a pressure of about pounds per square inch, the overhead fraction contains butadiene of about 98 per cent purity of which a portion is continuously returned as liquidfreux, another being a product of the process. The kettle product vcontains only a small amount of butadiene and comprises primarily z-butene's. f

I claim:

1. A process for separating butadiene in a highly concentrated state from othernormal C4 1 -7 hydrocarbons, which comprises subjecting a hydrocarbon material comprised essentially of substantial proportions of each of normalbutane, 1-buten,,2butene, and butadiene., with the pro.-

portion of 2-butene being greater than the proportion oi butadiene. to fractional distillation in the presence of sulfur dioxide in amount suflicient to form minimum-boiling azeotropes with all of the normal butane and 1butene con/tained in said material but insufficient to form an azeotrope with the-majr portion of the 2-butene contained distillation to separate butadiene in a concentrated'state as a product. y 2. A process for separating butadiene in a I highly concentrated state from other normal C4 oxide to separate butadiene in a highly' concendioxide, passing the resulting solution of butenes.

hydrocarbons, which comprises subjecting a hydrocarbon material comprised essentially of substantial proportions of each of normal butane, 1butene, 2-butene, and butadiene, with the proportion of 2-butene being greater than the proportion of butadiene, to a rst fractional distillation in the presence of sulfur "dioxide, adding sulfur dioxide to said first fractional distillation in an amount suflicient to form minimum-boiling azeotropes with all of the normal butane and 1- butene contained in said material but insufiicient t form an azeotrope with the major portion of the 2butene contained in said material, removing as an overhead product from said first fractional distillation all of the azeotropes formed between said sulfur dioxide and the hydrocarbons con'- tained in said material, separating a sulfur dioxide-rich fraction from said overhead product and returning same to said first fractional distillation as a liquid reflux and as a part of said added sulfur dioxide, removing from said frac tional distillation a kettle product consisting,

essentially of 2-butene and butadiene and containing the major portion of said 2-butene and substantially free of sulfur dioxide and passing said kettle product to a second fractional distillation. and fractionally distilling said kettle productin said second fractional distillation in the absence of sulfur dioxide to produce a rst product consisting essentially of butadiene and a Vinsufficient to form an azeotrope with the major portion of the 2-butene contained in said mixture, removing from said first fractional distillation as an overhead product all of said azeotropes so formed by said sulfur dioxide, removing also from said first fractional distillation a kettle tratedv form from Z-butene.

.4; An improved process for recovering a. butadiene concentrate from an aliphatic' C4 hydrocarbon mixture which comprises treating an aliphatic C4 hydrocarbon mixture containing substantial proportions of Yeach of normal butane,

1butene, Z-butene, and butadiene, with the pro-- portion of 2-butene being greater than the proportion of butadiene, with liquid sulfur dioxide to selectively absorb and effect' a concentration of butenes and butadiene in said liquid sulfur and butadiene in said sulfur dioxide to a rst fractional distillation and fractionally'distilling the same in the presence of sulfur .dioxide in amount sufiicient to form azeotropes with all of the normal butane and 1butene contained in said. solution but insufficient to form an azeotrope with the major portion of the 2-butene, refmoving as an overhead product from said first fractional distillation all of the azeotropes formed with said sulfur dioxide, removing as a kettle product from'said rst fractional Adistillation a mixture consisting of a major portion of each of the 2-butene and butadiene present in said originai `aliphatic C4 hydrocarbon mixture and free from sulfur dioxide, 1butene and normal butane,

' and subjecting said kettle product to a second product consisting essentially of said butadiene and a major portion of said Z-butene, and fractionally distilling said kettle product in a second fractional distillation in the absence of sulfur difractional distillation in the absence of sulfur dioxide to produce a low-boiling overhead fraction consisting essentially of butadiene. Y

5. A process for separating butadiene in a highly concentrated state from other normal C4 hydrocarbons which comprises subjecting a hydrocarbon' material consisting essentially of substantial proportions ofeach of normal butane, 1butene, 2-butene, and butadiene to a first fractional distillation in a first distillation zone Ain the presence of sulfur dioxide, adding an addi'- tional quantity of 2-butene to said distillation as hereinafter recited, adding sulfur dioxide to said first fractional distillation in an amount sutilcient to form minimum-boiling azeotropes with all of the normal butane and 1butene contained in said material but insufiicient to form an azeotrope with the major portion of the 2-butene present in said first distillation zone, removing as an overhead product from said-first fractional distillation all of the azeotropes formed with said sulfur dioxide, separating a sulfur dioxide-rich fraction from said overhead product and returning same to said rst fractional distillation as a liquid reflux and as a part of said added sulfur dioxide, removing afkettle product .from said first fractional distillation consisting essentially of 2butene and butadiene and substantially free of sulfur dioxide and passing same to a second 'fractional distillation,'fractionally distilling said kettle product in said second fractional distillation in the absence of sulfur dioxide to produce an overhead product consisting essentially of butadiene and a kettle product consisting essentially of '2-butene, and returning a portion of said last-named kettle product to saidfirst fractional distillation.

6. A process for separating butadiene in a highly concentrated state from other normal C4 hydrocarbons; which comprises subjecting a hydrocarbon material containing about 7 per cent butadiene, about 25 per cent normal butenes of which about one-fourth is 1butene and threefourths Z-butenes, and about 68 per cent normal butane to a rst fractional distillation in a rst distillation column in the presence of sulfur d1- -9 oxide in an amount' at least suicient and not greater than about 10 per cent in excess of that suicient to formminimum boiling azeotropic mixtures withall of the normal butane and l-butene contained in said vi'naterial, under ,the conditions existing at the top of said column, recovering as aloweboiling fraction from said distillation a mixture comprising sulfur dioxide, normal butane and 1butene and no more than a minor amountof tranS-Z-butene, recovering as a high-boi1ing fraction a mixture substantially free from sulfur dioxide and comprising said butadiene and the major `portion of said Z-butenes, fractionally distilling said high-boiling mixture in a second distillation column, and recovering as a 1owboi1ing fraction butadiene substantially free from other C4 hydrocarbons; Y

7. A process for separating butadiene in a highly concentrated state from other normal C4 hydrocarbons, which comprises subjecting a hydrocarbon material comprising substantial proportions oi each of butadiene, 1-butene, 2-butenes and normal butane with thel amount of 2-butenes in excess of the amount ofbutadiene to a rst fractional distillation in a iirst distillation column in the presence of sulfur dioxide in an amountV at least suicient and not greater than about 10 per cent in excess of that suliioient to form minimum boiling azeotropic mixtures with al1 of the normal butane and 1butene contained in said material, under the conditions existing atv the top ofjsaid column, recovering as a Iow-boilL ing fraction from'said distillation a mixture comprising sulfur dioxide, normal butane and 1bu' tene and no more than a minor amount of trans- 2butene, recovering as a high-boiling fraction a mixture substantially free from sulfur dioxide and comprising said butadiene and 'the maior portion of said Z-butenes, fractionally distilling said high-boiling mixture and in a second distillation column, and recovering-as a low-boiling fraction butadiene substantially free from other C4 hydrocarbons. l

FREDERICK E. FREY. 

